1. Technical Field
The invention relates to pneumatic actuators and particularly to a two-piece actuator formed of two plastic members of different hardnesses which are welded together by a heated joint. More particularly, the invention relates to a pneumatic actuator which is expanded outwardly into engagement with a work-piece by introducing pressurized air into an interior chamber of the actuator.
2. Background Information
Pneumatic actuators and/or air springs are well known in the art and usually comprise an elastomeric or resilient sleeve or bellows which is mounted between a pair of spaced members for maintaining the members in the predetermined spacing, and/or for moving one of the members with respect to the other by applying a force as a function of the spacing and internal pressure, or for absorbing shock exerted on one or both of the members. Pneumatic actuators move one of a pair of spaced members by introducing a pressurized fluid, usually air, within a hollow cavity formed within the pneumatic actuator. These actuators have various configurations and are formed of various materials.
Other actuators include a flexible member which when depressed, forces air from within a hollow interior through a fluid line to a remote device which actuates a switch to perform a various function. Examples of such pneumatic control actuation or switches are shown in U.S. Pat. Nos. 4,754,107, 5,155,309, 5,461,207, 5881,917, 5,962,826, and 6,121,559. None of these actuators use the flexible top member for expanding outwardly to move a workpiece or perform a similar function, but are depressed to provide a signal or switching function.
One problem that exists with many of the known air actuators is that excess movement of the flexible top member towards a more rigid base can cause damage to the top member and especially to a sealed joint formed between the top member and the base which is required to form an airtight internal chamber.
These prior air actuators are generally assembled from three or more components which must be manufactured, inventoried, and subsequently assembled, all of which increase the cost of the final product.
Although these prior art actuators which are used for initiating and sending a signal may be satisfactory for their intended purpose, it is desirable to form a more inexpensive, lightweight, extremely durable pneumatic actuator having a low profile formed of only two pieces of molded plastic, one of which has a greater hardness than the other in order to provide movement to a workpiece engaged by the actuator.
The invention provides a pneumatic actuator preferably formed of only two members, each of which is formed of a plastic material such as polyurethane, with a rigid base and a flexible top member secured thereto by a hot seam welded joint.
Another feature of the invention is to provide the actuator with a stop located within the internal air chamber which extends either upwardly from the base or downwardly from the flexible top member to limit the movement of the flexible top member toward a collapsed position to prevent the workpiece from contacting and possibly damaging the welded joint between the flexible top member and rigid base.
Another aspect of the pneumatic actuator is to provide the flexible top member with an annular convolution which surrounds a work engaging central portion of the top member to provide increased flexibility to the top member and to assist it to return to an at-rest position. The profile of the annular convolution is also designed to reduce fatigue on the material and welded joint and increase the life thereof, and in which the convolution can be designed to regulate the effective area within the air chamber and thus the work characteristics achieved by the flexible top member.
A further feature of the invention is providing the flexible top member with a thickened central work engaging portion surrounded by one or more convolutions providing increased stiffness to the flexible top member without materially affecting the flexibility thereof.
The pneumatic actuator preferably has a hot welded joint joining the flexible top member to the base which extends along an upper peripheral edge of the base to enable the base and top member to be easily joined together with a relatively simple welding procedure.
A further feature of the invention is providing the base with an opening having either a barbed coupler molded therein for connecting to an air supply line, or having an opening adapted to receive a barbed metal coupler or an air supply line molded therein.
Another aspect of the invention is that the flexible top member will have a durometer within the range of 80-90 Shore A hardness and that the polyurethane base will have a durometer in the range of 50-80 Shore D hardness; and in which the actuator can easily operate with pressures around 30 psi and withstand greater pressures of approximately 50 psi.
Another feature of the invention is providing the base with mounting flanges integral with the base for receiving fasteners through formed openings therein for easily mounting the rigid base to a supporting structure.
A further feature of the invention is providing the base and top members with various configurations such as oval, circular, oblong, etc.